HIV-1 Coreceptor Tropism, Proviral DNA

Test code(s) 91299

Question 1. What is HIV tropism?

Tropism refers to the type of cytokine coreceptor used by HIV-1 when infecting the host cell. The viruses in most (>80%) treatment-naïve patients use the CCR5 (R5) coreceptor.1 Conversely, the viruses in up to 50% of treatment-experienced patients use either the CXCR4 (X4) coreceptor or both coreceptors (ie, R5 and X4).2 Viruses that use both coreceptors are called dual-mixed (D/M) viruses.

Question 2. What is a coreceptor tropism test, and when should I consider one?

A coreceptor tropism test determines whether a patient exclusively harbors R5-tropic virus or has X4-tropic or D/M virus. Patients who exclusively harbor R5-tropic virus can be treated with CCR5 antagonists such as maraviroc (Selzentry®). CCR5 antagonists block R5 viruses from binding to the CCR5 coreceptor and infecting cells. CCR5 antagonists are ineffective in patients with X4 or D/M virus. Thus, coreceptor tropism testing can help determine patient eligibility for CCR5 antagonist therapy.

A coreceptor tropism test should be performed when the use of a CCR5 antagonist is being considered.3,4 Coreceptor tropism testing might also be considered for patients who exhibit virologic failure while taking a CCR5 inhibitor.3,4 See also Question 6.

Question 4. What is a proviral DNA tropism test?

A proviral DNA tropism test determines the tropism of HIV-1 DNA that has integrated into the host genome of infected T-lymphocytes. Proviral HIV-1 DNA persists despite suppressive antiviral therapy and therefore is present when plasma viral RNA is low or undetectable. Whole-blood or peripheral blood mononuclear cells (PBMC), rather than plasma, should be submitted for this test.

Although HIV-1 X4 sequences are more commonly found in proviral DNA than RNA, several studies have found a high degree of correlation between proviral DNA tropism and RNA tropism. For example:

Soulie et al determined proviral DNA tropism in a genotype assay and compared results to archived RNA tropism data from treatment-experienced patients with undetectable plasma viral loads. The authors saw no change in viral tropism over a median of 4 years in 92.9% (119/128) of these patients and concluded genotypic proviral DNA tropism could be used to determine viral tropism.5

Question 6. When should I consider a proviral HIV-1 DNA tropism test?

U.S. guidelines indicate that proviral testing can be used to determine tropism in patients with undetectable plasma viral load, but they note that the clinical utility of this approach has not yet been determined.3 The European tropism testing guidelines recommend proviral DNA tropism testing for patients with a low (<1000 copies/mL) or undetectable plasma viral load when they are being considered for maraviroc therapy.7

Proviral DNA tropism testing may be appropriate for successfully treated patients seeking to switch to a new regimen that includes a CCR5 antagonist.

Question 7. How do you perform a genotypic proviral DNA tropism test?

We first extract DNA from whole blood. PCR amplification of DNA in the V3 loop region of the HIV-1 envelope gene is performed in triplicate and the replicates are pooled for ultradeep sequencing (UDS). Tropism is then determined by bioinformatic analysis of the V3 loop sequence.

Question 8. What is the turnaround time for the proviral DNA tropism test?

The turnaround time is approximately one week.

Question 9. How are results from the proviral DNA tropism test reported?

This FAQ is provided for informational purposes only and is not intended as medical advice. A clinician’s test selection and interpretation, diagnosis, and patient management decisions should be based on his/her education, clinical expertise, and assessment of the patient.